Angiogenesis (or neovascularization), the development of blood vessels, plays an important role in embryonic development, in the inflammatory response, in the development of metastases (tumor induced angiogenesis or TIA), in diabetic retinopathy, in the formation of the arthritic panus and in psoriasis. In tumor angiogenesis, for example, capillary sprouts are formed, their formation being induced by a group of tumor cells. These sprouts eventually develop into a microcirculatory network within the tumor mass. There are two principle types of tumor angiogenesis in terms of the events which follow implantations of metastatic seedlings on surfaces and in organs.
The first or primary angiogenesis is the initial vascularization of the mass of multiplying tumor cells and is regarded as an essential prerequisite for the survival and further growth of a metastatic deposit.
The second is a continuing or secondary angiogenesis and is the phenomenon which occurs in waves at the periphery of a growing tumor mass. This second angiogenesis is essential for the accretion of new microcirculatory territories into the service of the expanding and infiltrating tumor.
It is apparent that a chemical which would inhibit angiogenesis, either by competitively inhibiting an angiogenesis factor or by some other mechanism, would have an adverse effect upon the growth of tumors, on the development of retinopathy or rheumatoid arthritis, or on the development of the psoriatic lesion.